The Transgenic Mouse/Gene Targeting Core will generate transgenic mice by microinjection of gene constructs into fertilized mouse eggs to investigate skeletal development. The transgenic founders will be delivered to the individual Program investigators for subsequent analysis. All of the four projects propose to generate transgenic mice with a series of gene constructs. In addition, this Core will generate ES cell lines carrying mutations in cartilage and bone development genes studies by the Program Investigators. Gene targeting constructs generated by the Program Investigators will be electroporated into mouse ES cells and culture under selective conditions to enrich for homologous recombinants. The resulting ES cell colonies will be picked, expanded, and split for temporary freeze and DNA preparation. DNA will be isolated and restricted with the appropriate enzymes. The restricted DNA will then be delivered to the Project Investigators for subsequent Southern analysis. Once identified, the Core will expand targeted clones for freeze down in nitrogen. The Core will inject targeted ES cell clones into blastocysts to generate mouse chimeras. The resulting mouse chimeras will be delivered to the individual Program Investigators for subsequent analysis. All of the projects propose to generate mice with targeted mutations. The Transgenic Mouse/Gene Targeting Core represents an essential component of this Program Project.